EPLIN is a gene that is transcriptionally downregulated in cancer cells. It encodes a novel LIM domain protein that co-localizes with the cytoskeletal structures. There are two known isoforms of EPLIN (alpha and beta), generated by an alternative promoter usage from a single copy gene located in chromosome 12q13. The expression of EPLIN is altered in a number of epithelial cancer cells, including several prostate cancer cell lines, xenografts, and tumors. Overexpression of EPLIN can alter actin fibers in the cell and inhibit anchorage independent growth of NIH3T3 cells transformed by Cdc42 or EWS/Fli-1. Purified EPLIN can bind filamentous actin and alter actin polymerization in vitro. The precise function of EPLIN and the relationship between EPLIN expression and transformation are not known. However, the known characteristics of EPLIN suggest that this cytoskeleton-associated protein may play a role in the regulation of the cytoskeleton. We believe that EPLIN functions to regulate the actin cytoskeleton in the cell by linking actin filaments to other structural or regulatory proteins. The disruption of EPLIN would therefore alter cytoarchitecture and impair cell-cell and/or cell-matrix interaction. We postulate that abnormalities in EPLIN could potentially play a role during progression of cancer by disrupting the organization of epithelial glands and promoting cell migration. The specific aims of this grant will test our ideas by studying (i) biochemical properties of EPLIN; (ii) function of EPLIN in normal and cancer cells; (iii) function of EPLIN during embryogenesis and in tissue homeostasis.